1. Field of the Invention
This invention generally relates to regenerative cells derived from a wide variety of tissues, and more particularly, to adipose-derived regenerative cells (e.g., stem and/or progenitor cells), methods of using adipose-derived regenerative cells, compositions containing adipose-derived regenerative cells, and systems for preparing and using adipose-derived regenerative cells which are used to treat renal diseases and disorders, e.g., acute tubular necrosis related diseases and disorders.
2. Description of the Related Art
Acute renal failure (ARF) is defined as an abrupt or rapid decline in renal (kidney) function. ARF occurs when high levels of uremic toxins, i.e., waste products of the body's metabolism, accumulate in the blood, and the kidneys are unable to excrete the requisite amount of the toxins through the urine. Since only one kidney is required to adequately filter blood, the onset of ARF generally indicates that both kidneys are failing to perform as needed.
ARF can occur in three clinical settings which are named for their location within the renal system, i.e., prerenal ARF, intrinsic ARF and postrenal ARF. Prerenal ARF is an adaptive response to severe volume depletion and hypotension and is characterized by structurally and functionally intact nephrons. Postrenal ARF is the result of an obstruction to the passage of urine. Intrinsic ARF is generally the most harmful form of ARF because it is a response to cytotoxic insults to the kidney and results in structural and functional damage that may be irreversible.
In the hospital setting, the most common cause of intrinsic ARF is acute tubular necrosis (ATN). ATN is the death of tubular cells. Tubules are extremely active structures in the kidney. They transport urine to the ureters and, in the process, alter the urine and its chemicals. Studies have shown that for every 200 liters of fluid that is filtered across the glomeruli, 99% is reabsorbed by the tubules. ATN, or death of tubular cells, occurs when the cells do not get enough oxygen (ischemic ATN) or when the cells have been exposed to a toxic drug or molecule (nephrotoxic ATN). Ischemic ATN is the most common cause of ARF in the hospital setting because hospital patients often have acute medical problems that limit the oxygen supplied to the tubules or that cause tubular hypoperfusion (decreased blood flow) (Thadhani R, Pascual M, Bonventre J V. Acute Renal Failure. N. Engl J. Med. 334:1448-1460).
ARF is the most common cause of death in hospitalized patients in the United States. Part of the reason for this mortality rate lies in the limited ability of the kidney tubular cells to repair themselves following ischemic damage. Thus, ARF patients often suffer from irreversibly damaged kidneys. Although, renal replacement therapies (RRTs), i.e., dialysis, can effectively treat life-threatening complications of ARF such as seizures, bleeding and coma, other risk factors prevalent in hospitalized patients (such as advanced age and underlying diseases) continue to cause a high mortality rate despite the availability of RRTs.
An alternative to transplant therapy is the use of regenerative medicine to repair and regenerate damaged renal cells, e.g., tubular cells. Regenerative medicine harnesses, in a clinically targeted manner, the ability of stem cells (i.e., the unspecialized master cells of the body) to renew themselves indefinitely and develop into mature specialized cells. For example, adult stem cells (ASCs) from bone marrow have been used in preclinical studies for the treatment of ATN (Kale S. et al. Bone Marrow Stem Cells Contribute to Repair of the Ischemically Injured Renal Tubule. JCI. 112:42-49, 2003; Poulsom R, et al. Bone marrow contributes to renal parenchymal turnover and regeneration. J Pathol; 195:229-235. 2001).
However, although ASC populations have been shown to be present in one or more of bone marrow, skin, muscle, liver and brain (Jiang et al., 2002b; Alison, 1998; Crosby and Strain, 2001), their frequency in these tissues is low. For example, mesenchymal stem cell frequency in bone marrow is estimated at between 1 in 100,000 and 1 in 1,000,000 nucleated cells (D'Ippolito et al., 1999; Banfi et al., 2001; Falla et al., 1993). Similarly, extraction of ASCs from skin involves a complicated series of cell culture steps over several weeks (Toma et al., 2001) and clinical application of skeletal muscle-derived ASCs requires a two to three week culture phase (Hagege et al., 2003). Thus, any proposed clinical application of ASCs from such tissues requires increasing cell number, purity, and maturity by processes of cell purification and cell culture.
Although cell culture steps may provide increased cell number, purity, and maturity, they do so at a cost. This cost can include one or more of the following technical difficulties: loss of cell function due to cell aging, loss of potentially useful non-stem cell populations, delays in potential application of cells to patients, increased monetary cost, and increased risk of contamination of cells with environmental microorganisms during culture. Recent studies examining the therapeutic effects of bone-marrow derived ASCs have used essentially whole marrow to circumvent the problems associated with cell culturing (Horwitz et al., 2001; Orlic et al., 2001; Stamm et al., 2003; Strauer et al., 2002). The clinical benefits, however, have been suboptimal, an outcome almost certainly related to the limited ASC dose and purity inherently available in bone marrow.
Recently, adipose tissue has been shown to be a source of ASCs (Zuk et al., 2001; Zuk et al., 2002). Adipose tissue (unlike marrow, skin, muscle, liver and brain) is comparably easy to harvest in relatively large amounts with low morbidity (Commons et al., 2001; Katz et al., 2001b). Suitable methods for harvesting adipose derived ASCs, however, are lacking in the art. The existing methods suffer from a number of shortcomings. For example, the existing methods lack partial or full automation, a partial or completely closed system, disposability of components, etc.
Given the tremendous therapeutic potential of adipose derived ASCs for regenerating and repairing renal cells, there exists a need in the art for a method for harvesting cells from adipose tissue that produces a population of adult stem cells with increased yield, consistency and/or purity and does so rapidly and reliably with a diminished or non-existent need for post-extraction manipulation.